X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Mon, 27 Feb 2006 00:21:59 -0500 Message-ID: X-Original-Return-Path: Received: from smtp105.sbc.mail.mud.yahoo.com ([68.142.198.204] verified) by logan.com (CommuniGate Pro SMTP 5.0.8) with SMTP id 998778 for lml@lancaironline.net; Sun, 26 Feb 2006 13:23:52 -0500 Received-SPF: none receiver=logan.com; client-ip=68.142.198.204; envelope-from=elippse@sbcglobal.net Received: (qmail 40082 invoked from network); 26 Feb 2006 18:23:07 -0000 Received: from unknown (HELO Computerroom) (elippse@sbcglobal.net@66.122.69.190 with login) by smtp105.sbc.mail.mud.yahoo.com with SMTP; 26 Feb 2006 18:23:07 -0000 X-Original-Message-ID: <000501c63b01$b20a8dc0$be457a42@Computerroom> From: "Paul Lipps" X-Original-To: Subject: spinner-cowl gap X-Original-Date: Sun, 26 Feb 2006 10:22:58 -0800 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0002_01C63ABE.9DEF22D0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.2180 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 This is a multi-part message in MIME format. ------=_NextPart_000_0002_01C63ABE.9DEF22D0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable When my plane was inspected by FAA for its Airworthiness, the = inspector noted the minimal clearance between my spinner and the = cowling; it measured .010" to .015". He asked me if that would not allow = it to rub. I said that when I pull power in flight and the prop is = pushed back, it will rub, but not for very long. Think abradable seals = on jet engine fan and compressor blades. Now when I pull forward on the = prop, it's about .03" to .05". Why make it bigger? Engine cooling air = from the high pressure plenum tries to come forward around the = crankshaft and exit radially through the gap. This causes a flow that = disrupts the smooth flow from the spinner and causes it to turbulate = back on to the cowling. It is actually preferable to have the cowling = 1/8" to 1/4" larger in diameter just behind the spinner with that = portion forming a "quarter-round". That forms a Coanda surface which = will turn the radial flow 90 degrees to the rear. It is the same = principle which is used to decrease drag on the horizontal surface by = enlarging and rounding the leading edge of the elevator (ailerons, too) = to 10% greater thickness than the stab immediately ahead of it, to cause = the stab-elevator gap flow to turn to the rear. See Hoerner's F.D. Drag, = P. 5-13, Fig. 28 and Stinton's "The Design of the Airplane", P. 444, = Fig. 12.9d. ------=_NextPart_000_0002_01C63ABE.9DEF22D0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
    When my plane was inspected = by FAA for=20 its Airworthiness, the inspector noted the minimal clearance between my = spinner=20 and the cowling; it measured .010" to .015". He asked me if that would = not allow=20 it to rub. I said that when I pull power in flight and the prop is = pushed=20 back, it will rub, but not for very long. Think abradable seals on = jet=20 engine fan and compressor blades. Now when I pull forward on the = prop, it's=20 about .03" to .05". Why make it bigger? Engine cooling air from the high = pressure plenum tries to come forward around the crankshaft and exit = radially=20 through the gap. This causes a flow that disrupts the smooth flow from = the=20 spinner and causes it to turbulate back on to the cowling. It is = actually=20 preferable to have the cowling 1/8" to 1/4" larger in diameter just = behind the=20 spinner with that portion forming a "quarter-round". That forms a Coanda = surface=20 which will turn the radial flow 90 degrees to the rear. It is the same = principle=20 which is used to decrease drag on the horizontal surface by enlarging = and=20 rounding the leading edge of the elevator (ailerons, too) to 10% greater = thickness than the stab immediately ahead of it, to cause the = stab-elevator gap=20 flow to turn to the rear. See Hoerner's F.D. Drag, P. 5-13, Fig. 28 and=20 Stinton's "The Design of the Airplane", P. 444, Fig.=20 12.9d.
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